feat(HttpResponse): support explicitly empty response body via null generic type

src/core/HttpResponse.ts

@@ -9,18 +9,16 @@ export interface HttpResponseInit extends ResponseInit {
   type?: ResponseType
 }
 
-declare const bodyType: unique symbol
+const bodyType: unique symbol = Symbol('bodyType')
 
-export interface StrictRequest<BodyType extends DefaultBodyType>
-  extends Request {
+export interface StrictRequest<BodyType extends JsonBodyType> extends Request {
   json(): Promise<BodyType>
 }
 
 /**
  * Opaque `Response` type that supports strict body type.
  */
-export interface StrictResponse<BodyType extends DefaultBodyType>
-  extends Response {
+interface StrictResponse<BodyType extends DefaultBodyType> extends Response {
   readonly [bodyType]: BodyType
 }
 
@@ -35,10 +33,15 @@ export interface StrictResponse<BodyType extends DefaultBodyType>
  *
  * @see {@link https://mswjs.io/docs/api/http-response `HttpResponse` API reference}
  */
-export class HttpResponse extends Response {
-  constructor(body?: BodyInit | null, init?: HttpResponseInit) {
+export class HttpResponse<BodyType extends DefaultBodyType>
+  extends Response
+  implements StrictResponse<BodyType>
+{
+  [bodyType]: BodyType = null as any
+
+  constructor(body?: NoInfer<BodyType> | null, init?: HttpResponseInit) {
     const responseInit = normalizeResponseInit(init)
-    super(body, responseInit)
+    super(body as BodyInit, responseInit)
     decorateResponse(this, responseInit)
   }
 
@@ -51,7 +54,7 @@ export class HttpResponse extends Response {
   static text<BodyType extends string>(
     body?: NoInfer<BodyType> | null,
     init?: HttpResponseInit,
-  ): StrictResponse<BodyType> {
+  ): HttpResponse<BodyType> {
     const responseInit = normalizeResponseInit(init)
 
     if (!responseInit.headers.has('Content-Type')) {
@@ -68,7 +71,7 @@ export class HttpResponse extends Response {
       )
     }
 
-    return new HttpResponse(body, responseInit) as StrictResponse<BodyType>
+    return new HttpResponse(body, responseInit)
   }
 
   /**
@@ -78,9 +81,9 @@ export class HttpResponse extends Response {
    * HttpResponse.json({ error: 'Not Authorized' }, { status: 401 })
    */
   static json<BodyType extends JsonBodyType>(
-    body?: NoInfer<BodyType> | null,
+    body?: NoInfer<BodyType> | null | undefined,
     init?: HttpResponseInit,
-  ): StrictResponse<BodyType> {
+  ): HttpResponse<BodyType> {
     const responseInit = normalizeResponseInit(init)
 
     if (!responseInit.headers.has('Content-Type')) {
@@ -100,10 +103,7 @@ export class HttpResponse extends Response {
       )
     }
 
-    return new HttpResponse(
-      responseText,
-      responseInit,
-    ) as StrictResponse<BodyType>
+    return new HttpResponse(responseText as BodyType, responseInit)
   }
 
   /**

src/core/handlers/RequestHandler.ts

@@ -3,7 +3,7 @@ import { getCallFrame } from '../utils/internal/getCallFrame'
 import { isIterable } from '../utils/internal/isIterable'
 import type { ResponseResolutionContext } from '../utils/executeHandlers'
 import type { MaybePromise } from '../typeUtils'
-import { StrictRequest, StrictResponse } from '..//HttpResponse'
+import type { StrictRequest, HttpResponse } from '..//HttpResponse'
 
 export type DefaultRequestMultipartBody = Record<
   string,
@@ -40,7 +40,7 @@ export type ResponseResolverReturnType<
 > =
   | ([ResponseBodyType] extends [undefined]
       ? Response
-      : StrictResponse<ResponseBodyType>)
+      : HttpResponse<ResponseBodyType>)
   | undefined
   | void
 
@@ -122,7 +122,7 @@ export abstract class RequestHandler<
     MaybeAsyncResponseResolverReturnType<any>,
     MaybeAsyncResponseResolverReturnType<any>
   >
-  private resolverGeneratorResult?: Response | StrictResponse<any>
+  private resolverGeneratorResult?: Response | HttpResponse<any>
   private options?: HandlerOptions
 
   constructor(args: RequestHandlerArgs<HandlerInfo, HandlerOptions>) {
@@ -326,7 +326,7 @@ export abstract class RequestHandler<
 
           // Clone the previously stored response from the generator
           // so that it could be read again.
-          return this.resolverGeneratorResult.clone() as StrictResponse<any>
+          return this.resolverGeneratorResult.clone() as HttpResponse<any>
         }
 
         if (!this.resolverGenerator) {

src/core/passthrough.ts

@@ -1,4 +1,4 @@
-import type { StrictResponse } from './HttpResponse'
+import type { HttpResponse } from './HttpResponse'
 
 /**
  * Performs the intercepted request as-is.
@@ -14,12 +14,12 @@ import type { StrictResponse } from './HttpResponse'
  *
  * @see {@link https://mswjs.io/docs/api/passthrough `passthrough()` API reference}
  */
-export function passthrough(): StrictResponse<any> {
+export function passthrough(): HttpResponse<any> {
   return new Response(null, {
     status: 302,
     statusText: 'Passthrough',
     headers: {
       'x-msw-intention': 'passthrough',
     },
-  }) as StrictResponse<any>
+  }) as HttpResponse<any>
 }

test/typings/http.test-d.ts

@@ -55,6 +55,54 @@ it('returns plain Response withouth explicit response body generic', () => {
   })
 })
 
+it('returns HttpResponse with URLSearchParams as response body', () => {
+  http.get('/', () => {
+    return new HttpResponse(new URLSearchParams())
+  })
+})
+
+it('returns HttpResponse with FormData as response body', () => {
+  http.get('/', () => {
+    return new HttpResponse(new FormData())
+  })
+})
+
+it('returns HttpResponse with ReadableStream as response body', () => {
+  http.get('/', () => {
+    return new HttpResponse(new ReadableStream())
+  })
+})
+
+it('returns HttpResponse with Blob as response body', () => {
+  http.get('/', () => {
+    return new HttpResponse(new Blob(['hello']))
+  })
+})
+
+it('returns HttpResponse with ArrayBuffer as response body', () => {
+  http.get('/', () => {
+    return new HttpResponse(new ArrayBuffer(5))
+  })
+})
+
+it('supports null as a response body generic argument', () => {
+  http.get<never, never, null>('/', () => {
+    return new HttpResponse()
+  })
+  http.get<never, never, null>('/', () => {
+    return new HttpResponse(
+      // @ts-expect-error Expected null, got a string.
+      'hello',
+    )
+  })
+  http.get<never, never, null>('/', () => {
+    return HttpResponse.json(
+      // @ts-expect-error Expected null, got an object.
+      { id: 1 },
+    )
+  })
+})
+
 it('supports string as a response body generic argument', () => {
   http.get<never, never, string>('/', ({ request }) => {
     if (request.headers.has('x-foo')) {